(a) Field of the Invention
This invention relates to moldable compositions and molded articles based on a sulphur component and a mineral aggregate and their preparation; more especially the invention is concerned with sulphur concretes, sulphur mortars and other sulphur-bound compositions of improved fracture toughness and in which crack propagation is retarded.
(b) Description of the Prior Art
Mixtures of mineral aggregate and sulphur, wherein the sulphur functions as a binder are termed sulphur concretes or sulphur mortars depending on the form of the mineral aggregate.
Articles which may be formed by casting such sulphur concretes include preformed concrete articles conventionally formed from concretes based on a mixture of a hydraulic cement, such as Portland cement, mineral aggregate and water together with various additives. Such articles include paving slabs, structural members, curbing, gutters, pipes and other cast products.
Sulphur mortars may be employed, for example, in the cementing or joining of pipe, bricks and tile, and as coating compositions to provide a protective surface.
Sulphur concretes and mortars display certain advantages, as compared with Portland cement, although they also suffer from certain disadvantages.
Sulphur is available in large quantities both as a by-product of oil refining and natural gas processing in the petroleum industry and from mining of sulphur deposits.
Although sulphur/mineral aggregate compositions, for example, sulphur concretes have many desirable properties, their use in some areas is hindered or limited by their low tensile strengths, brittle nature and poor fracture toughness, as a result of which the sulphur concretes tend to fracture abruptly when sharply impacted.
In brittle materials such as conventional sulphur concretes, cracks initiate as small tensile strains and the first crack usually leads to crack propagation and to complete failure of the material.
There is thus a need to improve the fracture toughness of conventional sulphur/mineral aggregate compositions, for example, sulphur concretes and to retard crack propagation in such compositions.
It has previously been proposed to include fibrous, flake or finely divided particulate material in sulphur based compositions. See, for example, U.S. Pat. Nos. 429,999; 1,438,840; 1,547,666; 1,557,231; 1,675,376; 3,306,000; 3,992,340; 3,997,355; 4,225,353 and 4,302,255.
Such fibrous, flake or finely divided particulate material has in particular been added in relatively small amounts as fillers or reinforcing agents. In the case of fibrous materials the afore-mentioned U.S. Patents require that the fibres be of short length, in particular not more than 1 inch and usually much shorter than 1 inch. U.S. Pat. No. 3,547,666, for example, employs asbestos fibres having an average length of about one-eighth of an inch or less; and U.S. Pat. No. 3,306,000 specifies that the fibres should not substantially exceed 0.50 inch in length because longer fibres tend to ball up in molten sulphur and do not give uniform compositions.
None of the prior U.S. Patents acknowledged above attribute improved fracture toughness or retardation of crack propagation to the fibrous, flake or finely divided particulate materials that they employ. In addition the prior U.S. Patents appear to consider that these distinct physical forms are equivalent.
It is an object of this invention to provide sulphur/mineral aggregate compositions, for example, sulphur concretes and mortars of improved fracture toughness and in which crack propagation is retarded.
It is a further object of this invention to provide a process for the manufacture of such sulphur/mineral aggregate compositions.